: His neck is thick and short. So it looks like his head sits right on his shoulders.

...and the implication is that he's not very bright. I'm not sure why there's an association between stupidity and necklessness (hmmm... bit dodgy that one) - but I'm guilty of making that association myself.

Only a couple of days ago I was chastising my big Yank about remarks he made about our local football code. I referred to players of Rugby League and possibly Grid Iron (but seeing they're always wearing all that armour it's hard to tell), as being neckless - and thus, by implication, brainless. Hence their inclination to just run and bash into each other and call it football.